In the bowl of a stand mixer fitted with the paddle attachment (or with a hand mixer), cream together the butter, sugar and salt until smooth. Add in the egg and mix until incorporated, then scrape down the sides. Add the flour and mix on low until just incorporated.
Wrap the dough in plastic wrap and flatten into a 1 inch thick disc. Place in the fridge for about two hours.
Remove the dough from the fridge and plastic wrap and allow it to sit at room temperature for about 15 minutes. Flour your work surface and rolling pin and roll out the dough until it’s ⅛-¼" thick. This dough is very forgiving, so if it cracks, you can patch it later. Roll the dough so it’s about 2 inches wider than the tart pan.
Transfer the dough to the pan and press it into the bottom, corners, and sides of the tart pan. Roll the rolling pin over the top of the pan to remove the excess dough, then use any of the scraps to patch holes or weak spots.
Transfer to the freezer for 15 minutes, and preheat the oven to 325℉. Remove the dough from the freezer and dock the bottom of the tart with a fork multiple times. Line the shell with parchment paper and fill completely with pie weights (or dried beans/rice).
Bake for 15 minutes to par-bake the crust, then remove to a wire rack to cool completely before adding the frangipane.